The plumbing and construction industries have for a long time understood the necessity of employing a trap, to act as a vapour barrier, between an open drain hole in a sink, for example, and a conduit to a sewer system or septic holding tank. Such traps are configured to retain (trap) an amount of water in a U-shaped bend which is sufficient to form the vapour barrier against noxious sewer gases entering into living space through an otherwise open drain. Such gasses are unhealthy and can cause sickness.
A conventional P-trap is formed from generally tubular drain fittings, which may be fabricated from either metal or plastic. A conventional trap is typically formed with the U bend to which is attached, for example, a 90 degree elbow at the outlet leg of the U. This elbow defines a generally horizontal outlet which can then be connected to appropriate drainage tubing which is in turn connected to a sewer or septic system for the disposal of liquid wastes. For P-traps made from plastic fittings the inlet leg of the U is typically solvent welded or frictionally coupled to a drain pipe which may for example extend down from a sink or bathtub drain. Typically between the 90 degree elbow and the U is a joint which may be either a solvent joint, or may be a detachable joint held together by a threaded connector. An example of prior art systems with threaded joints are found in U.S. Pat. Nos. 4,352,368 and 3,719,209. The other outlet end of the elbow is also typically solvent welded to the outflow drainage conduit.
Ideally such a P-trap is installed as follows. First the drain pipe from the sink and the drain conduit connecting the sink to the septic or sewer system are roughed in to an approximate location. The ends of these pipes will be generally in the same area, but not attached. Then the P-trap is installed between the free ends of the two pipes. The P-trap, comprising the elbow and the u shaped tube tightly threaded together, is first solvent welded at one end and then solvent welded at the other end. Then the threaded joint can be undone or relaxed if needed for further manipulation of the pipes.
However, what more typically happens is that the installer positions the P-trap in place between the free ends, and then trims the ends of the pipes to an appropriate length to accept the P-trap there-between. The location of the trap is often very awkward; the pipes may be crammed together under a sink in a vanity cabinet for example. So, typically, the installer will undo the threaded connection, and then solvent cement or glue or solvent weld, individually, the separated elbow and the u-shaped tube to respective free ends of the pipes. Then, the installer uses the threaded connector to draw the two components into a sealing relationship. While easy, this method is problematic. It is very difficult to ensure the two fittings are both attached perfectly in the same plane. Further because they are separated at the time they are attached, it is difficult to ensure that the ends are sufficiently close to permit the connector to easily couple the two ends together.
As a result it can be difficult to make a leakproof joint at the connection between the U-bend and the 90 degree elbow, because to do so requires precise positioning of the two solvent welded fittings relative to one another at a time when they are separated. According to preferred procedures, the threaded connection should be made tight between the elbow and the U-shaped bend before welding the components in place. However, where the elbow and U-shaped pipe are disconnected and each independently solvent welded onto their respective drain pipe connections misalignment usually occurs. The threaded coupler can compensate slightly for misalignment because of the compression provided by the threaded coupler onto a seal and the slight resiliency of a plastic pipe system. To rely on the inherent resiliency of the pipe system however essentially introduces a strain into the system. A P-trap joint which is under pressure may not seal properly or worse, it may seem sealed but over time due to the strain introduced by misalignment may fail at a later date. Alternatively, if the misalignment is large, the pressure generated by the threaded coupler as the components are clamped together can be enough to cause a cracking or opening of other drain pipe connections in the piping system.
Various types of couplings and connectors exist in the art, including the following:                U.S. Pat. No. 5,865,378 to Hollinshead et al;        U.S. Pat. No. 5,449,206 to Lockwood;        U.S. Pat. No. 3,891,246 to Hopper;        U.S. Pat. No. 3,243,209 to Chertok;        U.S. Pat. No. 3,034,809 to Greenberg;        U.S. Pat. No. 2,388,633 to Woody;        U.S. Pat. No. 1,829,101 to McGeorge;        U.S. Pat. No. 1,695,263 to Jacques;        U.S. Pat. No. 1,564,175 to Hoehn;        U.S. Pat. No. 1,475,090 to Taylor;        U.S. Pat. No. 1,187,642 to Milz;        U.S. Pat. No. 885,256 to Jones; and        U.S. Pat. No. 441,691 to McClellan.        
What is required, therefore, is a P-trap assembly which couples or connects to form a good liquid tight seal even when the components are slightly out of alignment without creating unacceptable stresses in either the P-trap assembly or any other part of the plumbing system.